Orientation sensor especially suitable for use in an underground boring device

ABSTRACT

An orientation sensor especially suitable for use in an underground device is disclosed herein. This orientation sensor includes a sensor housing defining a closed internal chamber, an arrangement of electrically conductive members in a predetermined positional relationship to one another within the chamber and a flowable material contained within the housing chamber and through which electrical connections between the electrically conductive members are made such that a comparison between an electrical property, specifically voltage, of a first combination of conductive members to the corresponding electrical property of a second combination of conductive members can be used to determine a particular orientation parameter, specifically pitch or roll of the sensor. In one embodiment disclosed herein, the electrically conductive members include an array of wires, as contrasted with plates or cylinders and in all of the embodiments disclosed herein in which the sensor functions as a pitch sensor, the conductive members are adjustably configured so that the sensor can be calibrated.

This is a Divisional application of application Ser. No. 08/986,294,filed on Dec. 6, 1997 now issued as U.S. Pat. No. 6,066,955 on May 23,2000 which is a divisional of application Ser. No. 08/564,587 filed Nov.29, 1995 now issued as U.S. Pat. No. 5,726,359 on Mar. 10, 1998, thedisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to an orientation sensorespecially suitable for use in an underground boring device, and moreparticularly to a number of specifically configured orientation sensorsand the way in which they are used to monitor pitch and/or roll of anobject such as a remotely controlled underground boring device.

Presently, there are a number of different known types of orientationsensors which have been designed especially for use in remote controlledunderground boring devices. One example can be found in U.S. Pat. No.4,674,579 (Geller). Another example can be found in U.S. Pat. No.4,714,118 (Baker). Still another example is described in Applicant's ownU.S. Pat. No. 5,155,442, 5,337,002, and 5,444,382. These patents areincorporated herein by reference. As will be seen hereinafter, thepresent invention is directed to a number of specifically improvedfeatures not disclosed or made obvious in view of the exemplified priorart.

SUMMARY OF THE INVENTION

As will be described in more detail hereinafter, the orientation sensordisclosed herein includes a sensor housing defining a housing chamber,an arrangement of electrically conductive members in a predeterminedpositional relationship to one another within the chamber, and aflowable material contained within the chamber and through whichelectrical connections between the electrically conductive members aremade such that a comparison between an electrical property, for examplevoltage, of a first combination of conductive members to thecorresponding electrical property of a second combination of conductivemembers is indicative of a particular orientation parameter,specifically pitch or roll, of the orientation sensor.

In one embodiment of the present invention, the arrangement ofelectrically conductive members includes first and second such membersdisposed at first and second spaced apart locations, respectively,within the chamber and at least one electrically conductive wiresupported by the housing and including a segment thereof disposed withinthe chamber at a location between the first and second electricalmembers. In this embodiment, the flowable material contained within thehousing chamber makes an electrical connection between the first andsecond conductive members and the wire segment such that the comparisonreferred to above is a ratio and this ratio is indicative of thedisplacement of the flowable material within the housing chamber,whereby the orientation sensor is capable of generating an outputvoltage indicative of the pitch position of the sensor. Preferably, thisembodiment of the present invention utilizes at least two wires whichare electrically connected together and which include segments thereofcrossing one another within the housing chamber, preferably within acommon plane centrally located between the first and second members andperpendicular to one another.

In a second embodiment of the present invention, the orientation sensordisclosed herein includes an arrangement of electrically conductivemembers including an array of at least four electrically unconnectedwire segments extending into the housing chamber in a predeterminedpositional relationship to one another within the housing and a flowablematerial contained within the housing chamber and through whichelectrical connections between the electrically conductive members aremade such that, for any given roll position of the sensor, apredetermined combination of the conductive members including certainones of the wire segments will be placed in contact simultaneously withthe flowable material so as to generate an output voltage correspondingto the combination and thereby represent the roll angle of the sensor.In a preferred configuration of this embodiment, the housing chamber isconfigured so as to define a central elongation axis and the array offour wire segments is located within the chamber in a substantiallycommon plane perpendicular to the elongation axis such that, if thehousing is oriented so that one of the wire segments is at a twelveo'clock position, the other three wire segments are positioned at three,six and nine o'clock, respectively, with respect to the position of thefirst mentioned wire segment.

In still another embodiment of the present invention, the arrangement ofelectrically conductive members include first, second, third, fourth,and fifth such members disposed at first, second, third, fourth, andfifth spaced apart locations, respectively, within an elongated housingchamber and along the chamber's elongation axis such that the first andthird members are disposed at substantially the ends of the chamber, thesecond member is disposed at substantially the center of the chamber,and the fourth and fifth are disposed on opposite sides of the secondmember between the latter and the first and third members, respectively.A flowable material is contained within this chamber and through whichelectrical connections between the electrically conductive members aremade (1) such that, in one mode of operation of the sensor, the ratiobetween an electrical property, for example voltage, of the first memberand second member to the corresponding electrical property of the thirdand second member is indicative of displacement of the flowable materialwithin the housing chamber, whereby the pitch sensor is capable ofgenerating a first mode output voltage which is also indicative of thepitch position of the sensor, and (2) such that, in a second mode ofoperation of the sensor, a ratio between the same electrical property ofthe fourth member and second member to the corresponding electricalproperty of the fifth member and the second member is also indicative ofdisplacement of the flowable material within the chamber, whereby thepitch sensor is capable of generating a second mode output voltage whichis also indicative of the pitch position of the sensor. In this latterembodiment, the various electrically conductive members could beconfigured as rings, cylinders, and/or plate members (in the case of thefirst and third members) and arrays of wire segments (in the case of thesecond, fourth, and fifth members).

In accordance with a further embodiment of the present invention, atleast three electrically conductive members are contained within anelongated housing chamber which also contains a flowable material of thetype described previously such that the sensor serves to measure pitch.In this embodiment, the three conductive members can be configured asrings, plates, cylinders and/or arrays of wire segments. Howeverirrespective of the particular configuration of each conductive member,means are provided for adjusting to a limited extent the positionalrelationship between these members along the elongation axis of thehousing chamber, whereby to calibrate the output voltage of the sensorwith respect to displacement of flowable material within the chamber. Ina preferred arrangement of this embodiment, the first and thirdconductive members are located at or near the end of the chamber and thesecond member is located approximately the center of the chamber,longitudinally speaking, and the adjusting means includes means formoving one of the first and third members along elongation axis to alimited extent, towards and away from the second member.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments of applicant's orientation sensor will bedescribed in more detail hereinafter in conjunction with the drawingswherein:

FIG. 1 is a partially broken away diagrammatic perspective view of anorientation sensor designed in accordance with one embodiment of thepresent invention;

FIG. 2 is a cross-sectional view of the sensor illustrated in FIG. 1,taken generally along line 2—2 in FIG. 1;

FIG. 3 is a longitudinal sectional view of the orientation sensor ofFIG. 1, taken generally along line 3—3 in FIG. 1;

FIG. 4 is a schematic diagram depicting how the orientation sensor ofFIG. 1 functions from an electrical standpoint;

FIG. 5 is an enlarged longitudinal sectional view of a modified sectionof the orientation sensor of FIG. 1, thereby establishing a secondembodiment of the present invention but specifically one which addscalibration to the sensor of FIG. 1;

FIG. 6 is a diagrammatic longitudinal sectional view of an orientationsensor designed in accordance with still another embodiment of thepresent invention, specifically one which also provides calibration in adifferent way than the embodiment illustrated in FIG. 5;

FIG. 7 is a diagrammatic illustration of still another modified versionof the orientation sensor of FIGS. 1-3 and specifically a version whichallows the sensor to act as a pitch and/or roll sensor,

FIGS. 8a, 8 b, & 8 c diagrammatically illustrates the way in which thesensor of FIG. 7 functions as a roll sensor;

FIG. 9 diagrammatically illustrates a modification to the sensorillustrated in FIG. 7;

FIG. 10 is a partially broken away diagrammatic perspective view of anorientation sensor designed in accordance with still a furtherembodiment of the present invention;

FIG. 11 diagrammatically illustrates the way in which the sensor of FIG.10 operates from an electrical standpoint;

FIGS. 12a, 12 b, & 13 diagrammatically illustrate the way in which thesensor of FIG. 10 functions as a pitch sensor; and

FIG. 14 is a diagrammatic longitudinal sectional view of a modifiedversion of the sensors of FIGS. 6 and 10.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, wherein like components are designated bylike reference numerals throughout the various figures, attention isfirst directed to FIGS. 1-4. These figures illustrate a pitch sensorwhich is designed in accordance with one embodiment of the presentinvention and which is generally designated by the reference numeral 10.Pitch sensor 10 is shown including a pitch sensor housing 12 defining anelongated closed internal chamber 14 which defines a central elongationaxis 16. In the embodiment illustrated, the cross-sectionalconfiguration of chamber 14 is circular, as best illustrated in FIG. 2,although it could be square, rectangular or any other reasonable shapeso long as it is compatible with the invention. As illustrated best inFIG. 1 in conjunction with FIG. 3, pitch sensor 10 is shown includingfirst and second electrically conductive plate members 18 and 20 fixedlymounted to housing 12, at least partially within and defining the endsof chamber 14.

Referring specifically to FIG. 2 in conjunction with FIG. 3, pitchsensor 10 is also shown including a third electrically conductive memberdesigned in accordance with one aspect of the present invention.Specifically, this third electrically conductive member includes twoelectrically conductive wires 22 and 24. Electrically conductive wire 22extends through diametrically opposed through holes 26 in housing 12 soas to include a segment 22 a disposed within chamber 14. In a similarmanner, electrically conductive wire 24 extends through cooperating,diametrically opposed through holes 28 such that a segment 24 a isdisposed within chamber 14 transverse to segment 22 a. In the specificembodiment illustrated, the two electrically conductive wire segments 22a and 24 a are positioned substantially within a common plane normal tothe elongation axis 16 of chamber 14 at a location approximatelycentrally located between the two electrically conductive end plates 18and 20 with wire segment 24 a extending perpendicular to wire segment 22a and such that their common crossing point is coincident withelongation axis 16. Through-holes 26 and 28 may be provided in anysuitable manner but are most economically provided by means of drilling,injection molding, or any suitable means.

For the reasons to be described below, the two electrically conductivewires 22 and 24 are permanently electrically connected together, forexample in the manner diagrammatically depicted in FIG. 2 wherein aseparate jump wire 30 connects together corresponding ends of the twowires. In that case, the other ends of the wires are held in place bysuitable means such as enlarged ends (as shown), crimping, glue, or thelike. As an alternative, a single wire could be threaded through allfour openings 22 and 24 in a crisscross fashion to accomplish the sameresult without having to use a jump wire 30.

Still referring to FIGS. 1-3, chamber 14 is partially filled with asuitable conductive fluid, for example, glycerin with a small quantityof saline solution added to provide for conductivity, selected asdescribed below and in Applicant's above recited patents. In order tofunction in the manner intended, chamber 14 is filled with conductivefluid 32 to a level at or just slightly above elongation axis 16 whenthe chamber is perfectly horizontal. That is, the fluid just covers wiresegment 24 a when the latter and the elongation axis extendhorizontally, as illustrated in FIG. 2. Considerations relating to thefluid level in the chamber will be further described at appropriatepoints hereinafter.

In order for pitch sensor 10 to function as a pitch sensor in theintended way, it is connected to a suitable drive circuit, for examplethe one illustrated in Applicant's above recited patents or a simplifiedversion could be provided, as illustrated in FIG. 4 and generallydesignated by the reference numeral 34. This simplified drive circuit isshown including an A/C voltage source 36 and a voltmeter 38 which areconnected to one another and to device 10 such that the device functionsas a voltage divider. Specifically, as illustrated in FIG. 4, one sideof the voltmeter 38 is connected to the two wires 22 and 24 by means ofterminal TC. The other side of the voltmeter is connected toelectrically conductive plate member 18 and to one side of voltagesource 36 which is also connected to member 18, all by means of terminalThe other side of the voltage source 36 is connected to electricallyconductive plate member 20 by means of terminal TR.

Having described pitch sensor 10 and drive circuit 34 from a structuralstandpoint, attention is now directed to the way in which the pitchsensor operates. In this regard, from an operational standpoint, it mayfunction in the manner described in Applicant's above recited patentsutilizing the drive circuit in those patents or, in fact, it couldfunction in the manner described in the Geller and Baker patents recitedabove utilizing their drive circuitry. Nevertheless, its operation willbe described here in conjunction in drive circuit 34. As statedimmediately above, the pitch sensor itself functions in this overallcircuitry as a voltage divider. If it is assumed for the moment that thepitch sensor is perfectly horizontal, electrically conductive fluid 32will cover the same amount of surface area of plate member 18 as platemember 20. As a result, the voltage applied across the pitch sensor,that is, from terminal TL at one end to terminal TR at the other end,will be divided precisely in half, that is, one half of the voltage willappear between terminal TL and terminal TC while the other half willappear between terminal TC and terminal TR. Thus, the voltage v1 and thevoltage v2 illustrated in FIG. 4 will be equal. If the pitch sensor ispivoted clockwise, for example, more of the surface area of member 20becomes covered with fluid 32 while less of the surface area of member18 is covered. As a result, the voltages v1 and v2 becomeproportionately dissimilar. Thus, by monitoring one of these voltages,for example the voltage v1, as illustrated, the pitch of the sensor canbe so monitored.

In the embodiment illustrated in FIGS. 1-3, pitch sensor 10 has beendescribed as including two wire segments 22 and 24 maintained in aperpendicular relationship to one another. It is to be understood thatthe present invention is not limited to this configuration. Indeed, oneor more wire segments could be utilized so long as at least one of thesegments is at all times in contact with conductive fluid 32 and thepitch sensor operates in the manner described. Thus, while the use of asingle wire segment is possible, it would only be practical where thepitch sensor itself has no roll component or at least the roll componentis controlled so as to insure that the single wire segment is always incontact with the fluid and this assumes the conductive fluid is filledless than half way within its chamber. It will always work with a singlewire if the chamber is filled more than half way irrespective of roll.The two perpendicular wire segments 22 a and 24 a, in the perpendicularconfiguration illustrated, insures that at least one wire segment willalways be in contact with fluid 32 when the latter is filled to thelevel describe. In this way, the pitch sensor operates independent ofroll. Moreover, pitch sensor 10 has been described using a conductivefluid so as to measure voltage by means of current flow through thefluid. In this and all the other sensor embodiments disclosed herein,the fluid could be dielectric fluid, for example glycerin, as contrastedwith conductive fluid, so that the voltage is measured by means ofrelative capacitance rather than relative resistance.

It is not suggested here that pitch sensor 10, as described above,functions as a roll independent pitch sensor in any way that isdifferent than those described in the above recited patents, from afunctional standpoint However, the utilization of electricallyconductive wires 22 and 24, as contrasted with rings or cylinders, makethe pitch sensor much more economical to manufacture than those in thepast.

Pitch sensor 10 has been described including electrically conductiveplate members 18 and 20 and wire segments 22 a and 24 a in a fixedpositional configuration. In accordance with another embodiment of thepresent invention, the sensor is designed so that this positionalconfiguration can be changed to provide the sensor with calibrationcapabilities. In particular, FIG. 5 illustrates a modified pitch sensor10′ which may be identical to sensor 10, except for its left hand endillustrated in FIG. 5. This end of sensor 10′ is shown including anelectrically conductive plate member 18′ which is longitudinallymovable, to a limited extent, within chamber 14′ defined by housing 12′.Note specifically that chamber 14′ includes a longitudinally extending,radially enlarged circumferential end section 40 which allows end plate18′ and a sealing ring 42 extending around the plate to slidably movelongitudinally while maintaining a seal around the interior of chamber14′ so as to prevent the leakage of electrically conductive fluid 32.Alternatively, plate 18′ could permit fluid to flow through it andsealing could be accomplished around shaft 44 using suitable sealingmeans (not shown). In this way, the electrically conductive plate 18′can be adjustably located between an extreme left hand position, asviewed in FIG. 5, and an extreme right hand position within the enlargedcircumferential end section 40. Movement of the end plate isaccomplished by means of a threaded shaft 44 disposed within acooperating threaded opening 46 through housing 12′. One end of thethreaded shaft is rotatedly coupled but otherwise fixed to plate member18′ while the other end carries an adjustment thumb wheel 48. Byrotating the thumb wheel in one direction, the threaded shaft movesforward into the housing causing the plate member to move with it.Movement of the thumb wheel in the opposite direction causes the shaftto move backward, bringing the plate member with it. With regard tosection 40, for purposes of symmetry, a similar section should beprovided at the other end of the chamber.

Having described pitch sensor 10′ structurally, attention is nowdirected to the way in which it can be calibrated or zeroed. One way todo this is to initially position the pitch sensor horizontally so thatthe voltage measured by voltmeter 38, that is, voltage v1 (see FIG. 4)should be precisely one-half the total voltage between terminals TL andTR. If it is, no calibration is necessary. However, if the measuredvoltage v1 is more or less than one-half the total voltage, then theadjustable conductive plate member 18′ should be moved either to theright or the left until the measured voltage v1 is precisely one-half ofthe total voltage, thereby calibrating the pitch sensor. Obviously, thepresent invention is not limited to moving electrically conductivemember 18′ specifically. The electrically conductive member on the otherside of the pitch sensor could be made adjustable alternatively or itcould be made adjustable along with member 18′ in order to get a greatercalibration range. Indeed, even the centrally located conductive membercould also be made longitudinally adjustable.

From an operational standpoint, pitch sensor 10″ functions in the sameway as previously described pitch sensors 10 and 10′. Specifically, thetwo cylindrical conductors 56 and 58 functionally correspond topreviously described plate members 18 and 20 and electrically conductivesection 62 of rod 60 corresponds functionally to the array of wiresegments 22 a and 24 a. From an electrical circuit standpoint, thecylinder 56 would be connected to the TL terminal of the circuit shownin FIG. 4, the cylinder 58 would be connected to the TR terminal and theelectrically conductive section 62 of rod 60 would be connected to theTC terminal, as diagrammatically illustrated in FIG. 6. Pitch sensor 10″can be calibrated in the same manner pitch sensor 10′. That is, thepitch sensor 10″ could first be positioned horizontally so that aninitial reading of voltage v1 (FIG. 4) could be taken. If this voltagereading is not precisely one-half of the total voltage between terminalsTC and TR., then the rod 60 could be adjusted longitudinally, either tothe left or the right as view in FIG. 6, until voltage v1 is preciselyone-half the total voltage.

All of the pitch sensors described thus far, that is, pitch sensors 10,10′, and 10″ are roll insensitive, that is, the measured output voltagev1 is independent of the roll orientation of the pitch sensor. FIG. 7illustrates still another orientation sensor 80 which is designed notonly to measure pitch, but is primarily designed to measure roll. Thisorientation sensor may be identical to the previously described pitchsensor 10, with one exception. In pitch sensor 10, the wire segments 22a and 24 a are connected together and the array is connected to theterminal TC, as illustrated best in FIG. 2. In the case of orientationsensor 80, its central electrically conductive arrangement is shownconsisting of four unconnected wire segments 82 a, 82 b, 82 c, and 82 ddisposed within chamber 14 in a common plane normal to the elongationaxis 16 of the chamber and centrally located between the ends of thechamber. Each wire segment 82 extends radially into chamber 14 not quiteto the center thereof. As illustrated in FIG. 7, these wire segmentsform the ends of longer wires which extend out of the housing throughcooperating through-holes, which like previously described through-holes26 and 28 (FIGS. 2 & 3) may be pre-drilled or otherwise provided. Asalso illustrated in FIG. 7, the four wire segments 82 a, 82 b, 82 c, and82 d are positioned relative to one another such that if wire segment 82a is at the twelve o'clock position, wire segments 82 b, 82 c, and 82 dare in the three o'clock, six o'clock, and nine o'clock positions,respectively. At the same time, the electrically conductive fluid 32described previously in conjunction with pitch sensor 10 fills slightlymore than half of chamber 14. Thus, when orientation sensor 80 isperfectly horizontal, as illustrated in FIG. 7, the electricallyconductive fluid just barely contains the three wire segments 82 b, 82c, and 82 d but not wire segment 82 a.

Still referring to FIG. 7, each of the wires including an end segment 82a-d extends through a conventional and readily providable multiplexor 84having as its output the terminal TC which functionally corresponds tothe same terminal in the circuitry of FIG. 4. Thus, by using multiplexor84, the voltage v1 (FIG. 4) can be successively monitored for thecombination of end plate members 18 and 20 (FIG. 3) and each individualwire segment 82 a-d In this way, the roll position of sensor 80 can bemonitored, as will be described immediately below in conjunction withFIGS. 8a-8 c.

Turning now to FIG. 8a, pitch sensor 80 is diagrammatically shown in itsFIG. 7 position, that is, extending horizontally with the four wiresegments 82 a-d in the twelve, three, six, and nine o′ clock positions,respectively. With the pitch sensor oriented in this manner, successivemeasurements of voltage v1 can be made for each of the wire segmentsusing multiplexor 84. In this case, a voltage will be measured for eachof the wire segments 82 b, c, and d because each of these latter wiresegments is in contact with the conductive fluid 32. However, no voltagewill appear between the wire segment 82 a and conductive plate member 18since wire segment 82 is not in contact with the conductive fluid and,hence, results in an open circuit. This tells the operator that the rollposition of the orientation sensor corresponds to FIG. 8a. Let it now beassumed that the sensor has rolled to the position illustrated in FIG.8b. Under this circumstance, it should be noted that only the wiresegments 82 b and 82 c are in contact with the electrically conductivefluid 32 and, hence, only v1 voltage values will be measured for wiresegments 82 b and 82 c, thereby indicating to the operator that the rollposition of the orientation sensor corresponds to the positionillustrated in FIG. 8b. Assume now that the orientation sensor rotatesfurther clockwise to the position shown in FIG. 8c. Under thesecircumstances, the wire segments 82 a, 82 b, and 82 c are now in contactwith the electrically conductive fluid 32 while wire segment 82 d isnot. Accordingly v1 voltages will be obtained for the former three wiresegments but not the latter one. Accordingly, the operator will be ableto tell that the orientation sensor corresponds to the positionillustrated in FIG. 8c. It should be clear that for any roll position ofsensor 80, at least two and at most three wire segments will makecontact with electrically conductive fluid 32 and, thus, the operatorcan monitor all roll positions by monitoring the v1 voltage associatedwith each of these wire segments.

Orientation sensor 80 has been described with respect to its ability tomonitor roll. It should be apparent that it can also monitor pitch inthe same way as sensors 10, 10′ and 10″ by monitoring the actualmagnitude of the v1 voltage associated with any of the wire segmentsthat is in physical contact with the fluid medium. Moreover, whileorientation sensor 80 functions as a roll sensor, its resolution islimited by the utilization of only four wire segments 82. Its resolutioncan be improved by adding additional wire segments, as illustrated, forexample, in FIG. 9. As seen there, a modified orientation sensor 80′ isshown. This modified orientation sensor is identical to sensor 80,except that sensor 80′ includes eight wire segments rather than four.For purposes of convenience, these latter wire segments are indicated assegments 1-8. The sensor is shown in a position corresponding to FIG. 8ain which wire segment 1 is in the twelve o'clock position while wiresegments 2-8 are in the following positions, respectively: one-thirty;three o'clock; four-thirty; six o'clock; seven-thirty; nine o'clock; andten-thirty. In the case of sensor 80′, with fluid 32 filling chamber 14to or just slightly above the half-way mark, at least four wire segmentswill simultaneously make contact with the fluid and at most five wiresegments will make contact. Thus, using the procedure described withrespect to sensor 80, the operator can determine to a greater accuracythe roll position of sensor 80′. Obviously the present invention is notlimited to the number of positions of these wires. For example, onecould use six equally spaced wires or even a single wire where you justwant to know if the device has rolled off a predetermined position. Alsothe length of the wire or wires is not critical so long as the devicefunctions in the intended manner.

Turning now to FIG. 10, attention is directed to a pitch sensor 86 whichis designed in accordance with a further embodiment of the presentinvention. This pitch sensor may be identical in all respects to pitchsensor 10, with one exception. Whereas pitch sensor 80 was describedincluding three conductive members, plate members 18 and 20 and wiresarray 22 a, 24 a, pitch sensor 86 includes five conductive members. Theyare the three conductive members just mentioned, that is, those formingpart of pitch sensor 10 plus fourth and fifth electrically conductivemembers 88 and 90. Both of these latter electrically conductive membersare in the form of electrically conductive screens positioned withinhousing chamber 14 on opposite sides of wire segment array 22 a, 24 alongitudinally between the latter and plate members 18 and 20respectively, in planes normal to the elongation axis 16. These screensare sufficiently porous to allow the electrically conductive fluidmedium 32 to flow freely therethrough, essentially as if they were notthere. As illustrated in FIG. 10, screen 88 is connected to an externalterminal TSL while screen 90 is connected to an external terminal TSRfor the reasons to be discussed below in conjunction with FIG. 11. Atthe same time, the plate members 18 and 20 are connected to terminals TLand TR, respectively, and the wire segment array 22 a, 24 a is connectedto terminal TC, in the manner described previously.

Turning now to FIG. 11, attention is directed to the circuit 34′ whichis used to operate pitch sensor 86 in a manner similar to the way inwhich circuit 34 (FIG. 4) operates pitch sensor 10. As seen in FIG. 11,circuit 34′ includes the same voltage source 36 and voltmeter 38 ascircuit 34. However, circuit 34′ also includes three switches, s1, s2,and s3. One side of voltmeter 38 is connected to the terminal TC, as incircuit 34, however its other side is alternatively connected betweenterminals TL and TSL by means of switch s1. At the same time, one sideof voltage source 36 is alternatively connected between the terminals TLand TSL by means of switch s2 while the opposite side of the voltagesource is alternatively connected between the terminals TSR and TR bymeans of switch s3.

With circuit 34′ described immediately above from a structuralstandpoint, attention is now directed to the way in which it operatesthe pitch sensor 86 in two different operating modes. With switch s1 inits TL position, switch s2 in its TL position, and switch s3 in its TRposition, circuit 34′ operates pitch sensor 86 in precisely the samemanner that circuit 34 operates pitch sensor 10, as describedpreviously. This first mode of operation is used, for example, when thepitch sensor is at a pitch angle between plus or minus 10% grade.However, when the pitch sensor moves outside this range, the switchess1, s2, and s3 can be moved to their alternate positions illustrated inFIG. 11. In this mode of operation, the voltmeter is connected betweenthe central wire segment array 22 a, 24 a and screen 88 and the voltagesource 36 is connect across this latter wire screen and wire screen 90.In this second mode of operation, the wire screens 88 and 90 replaceelectrically conductive members 18 and 20, thereby effectively reducingthe longitudinal length of the overall pitch sensor. In this mode, thev1 voltage being measure by the voltmeter 38 extends between screen 88and wire segment array 22 a, 24 a. This mode of operation is used, forexample when the pitch sensor is at an orientation greater than 10%grade. FIGS. 12a and 12 b illustrate the extreme positions of the pitchsensor 86 in its first mode of operation, that is, for example, between0% grade (FIG. 12a) and 10% grade (FIG. 12b), while FIG. 13 shows thepitch sensor operating in the second mode when it is at a pitch anglegreater than, for example 10% grade. The reason it is necessary to havethis second mode of operation is that at a certain point as the pitchsensor increases in pitch, none of the fluid makes contact with one ofthe end plate members, for example plate member 20, while the otherplate member is entirely in contact with the fluid at a number ofdifferent pitch points. Under these circumstances, as illustrated inFIG. 13, the first operating mode described above would be ineffective.

While pitch sensor 86 has been described including two modes ofoperation, it is to be understood that additional pairs of screenscorresponding to screens 88 and 90 could be utilized so as to increasethe number of modes of operation. Moreover, it is to be understood thatthe present invention is not limited to operating modes between theranges recited above. The positional relationship of the variousconductive members can be arranged to accommodate different graderanges. Further, it is to be understood that the present invention isnot limited to wire screens for members 88 and 90 but could utilizearrays of wire segments similar to the array 22 a, 24 a so long as theselatter members allow free flow of the fluid medium and accuratelyreflect the amount of surface area that contacts the fluid as in thecase of the screens or solid members 18 and 20. In addition, the rollmeasuring feature of sensor 80 could be incorporated into sensor 86 byreplacing wires 22 a, 24 a with the arrangement shown in FIGS. 8 or 9.Moreover, one or both end members 18 and 20 could be made to beadjustable as in the case of member 18′ (FIG. 5).

Finally, turning to FIG. 14, attention is directed to a pitch sensor 92which is designed in accordance with still a further embodiment of thepresent invention. Pitch sensor 92 is also a multi-mode pitch sensor andfunctions in essentially the same manner as pitch sensor 86 describedabove. However, rather than including electrically conductive end plates18 and 20, a central wire segment array 22 a, 24 a, and screens 88 and90, sensor 92 utilizes four electrically conductive cylindrical members94, 96, 98, and 100 and a central shaft 102. From an operationalstandpoint, cylindrical members 94 and 96 correspond to end plates 18and 20, respectively. Shaft 102 corresponds to the central wire segmentarray 22 a, 24 a and cylindrical members 98 and 100 correspond toscreens 88 and 90, respectively. From a structural standpoint,cylindrical members 94 and 96 correspond to cylindrical members 56 and58 forming part of overall pitch sensor 10″ and shaft 102 is identicalto shaft 60. Thus, shaft 102, like shaft 60 includes an electricallyconductive longitudinal section 104 located between dielectric segments106 and 108. The five electrically conductive segments of sensor 92 areconnected up to previously described circuit 34′ in the same manner aspitch sensor 86 and therefore operates in its first and second mode inthe same way. The operational difference between sensor 92 and sensor 86is that the former can be calibrated in the same manner as sensor 10″.

In the case of sensor 92, the central shaft could be replaced witheither the wire arrangement 22 a, 24 a or the wire arrangements shown inFIGS. 8 and 9. Also, this sensor could be made without the calibrationfeature.

What is claimed is:
 1. A pitch sensor capable of generating an outputvoltage indicative of fluid displacement within the pitch sensor,comprising: (a) a pitch sensor housing defining a closed, elongatedinternal chamber which itself defines a central elongation axis; (b)first, second and third electrically conductive members disposed atfirst, second and third spaced apart locations, respectively, withinsaid chamber and along said elongation axis such that said second memberis disposed between said first and third members; (c) a flowablematerial contained within said chamber and through which electricalconnections between said electrically conductive members are made bysaid flowable material contacting portions of said first, second andthird electrically conductive members such that a first ratio of anelectrical property between the first member and the second member tothe corresponding electrical property between the third member and thesecond member is indicative of displacement of said flowable materialwithin said chamber and the pitch sensor uses said first ratio togenerate the output voltage indicative of such material displacement;and (d) means for adjusting to a limited extent the positionalrelationship between said first, second and third members along saidelongation axis, whereby to calibrate the output voltage of the pitchsensor with respect to displacement of said flowable material withinsaid chamber.
 2. A pitch sensor according to claim 1 wherein saidadjusting means includes means for moving one of said first and thirdmembers along said elongation axis to a limited extent towards and awayfrom said second member.
 3. A pitch sensor according to claim 1 whereinsaid adjusting means includes means for moving said second member alongsaid elongation axis to a limited extent towards and away from each ofsaid first and third members.
 4. A pitch sensor according to claim 1including a fourth electrically conductive member disposed at a fourthlocation within said chamber and along said elongation axis between saidfirst and second members and a fifth electrically conductive memberdisposed at a fifth location within said chamber and along saidelongation axis between said second member and said third member, saidsecond, fourth and fifth members being positioned relative to oneanother for contacting the flowable material such that, in a second modeof operation of the pitch sensor, a second ratio of said electricalproperty between the second and fourth members to the correspondingelectrical property between the second and fifth members is indicativeof displacement of said flowable material within said chamber and thepitch sensor uses said second ratio to generate the output voltageindicative of such material displacement.
 5. A pitch sensor according toclaim 4 wherein said fourth and fifth members are wire screens.
 6. Apitch sensor according to claim 1 wherein said first and thirdelectrically conductive members are co-axial rings positionedconcentrically around the elongation axis of said chamber and whereinsaid pitch sensor includes a rod extending along the entire length ofsaid chamber coincident with its elongation axis, said rod having outersegments thereof which are not electrically conductive and a centralsegment therebetween which is electrically conductive and which servesas said second electrically conductive member.
 7. A pitch sensoraccording to claim 1 wherein all of said electrically conductive membersare co-axial rings positioned concentrically around the elongation axisof said housing chamber.
 8. A pitch sensor capable of generating anoutput voltage indicative of fluid displacement within the pitch sensor,comprising: (a) a pitch sensor housing defining a closed, elongatedinternal chamber which itself defines a central elongation axis; (b)first, second, third, fourth and fifth electrically conductive membersdisposed at first, second, third, fourth and fifth spaced apartlocations, respectively, within said chamber and along said elongationaxis such that said first and third members are disposed atsubstantially the ends of said chamber, said second member is disposedat substantially the center of the chamber, and said fourth and fifthmembers are disposed on opposite sides of said second member between thelatter and said first and third members, respectively; and (c) aflowable material contained within said chamber and through whichelectrical connections between said electrically conductive members aremade such that, in one mode of operation of the pitch sensor, a firstratio of an electrical property between the first member and the secondmember to the corresponding electrical property between the third memberand the second member is indicative of displacement of said flowablematerial within said chamber and the pitch sensor uses said first ratioto generate the output voltage indicative of such material displacement,and such that, in a second mode of operation of the pitch sensor, asecond ratio of an electrical property between the fourth member and thesecond member to the corresponding electrical property between the fifthmember and the second member is indicative of displacement of saidflowable material within said chamber and the pitch sensor uses saidsecond ratio to generate the output voltage indicative of such materialdisplacement.
 9. A method of calibrating a pitch sensor having (i) apitch sensor housing defining a closed internal chamber, (ii) anarrangement of electrically conductive members in a predeterminedpositional relationship to one another within the chamber, and (iii) aflowable material contained within said chamber and through whichelectrical connections between said electrically conductive members aremade such that a ratio of an electrical property between a certaincombination of said members to the corresponding electrical propertybetween a different combination of said members is indicative ofdisplacement of said flowable material within said chamber and the pitchsensor uses said ratio to generate the output voltage indicative of suchmaterial displacement, said method comprising the steps of: (a)generating an initial output voltage indicative of the displacement ofsaid flowable material with the pitch sensor housing at a predeterminedorientation and said electrically conductive members in fixed positionsrelative to one another; (b) determining whether said initial outputvoltage actually indicates accurately what the displacement of saidflowable material should be with the pitch sensor housing at saidpredetermined orientation; and (c) if said initial output voltage doesnot accurately indicate what the displacement of said flowable materialshould be with the pitch sensor housing at said predeterminedorientation, adjusting the positional relationship of said electricallyconductive member and then repeating these steps (a), (b) and (c) untilthe output voltage does accurately indicate what the displacement ofsaid flowable material should be with the pitch sensor housing at saidpredetermined orientation.
 10. A method of monitoring the pitch of anobject in at least two operating modes, comprising the steps of: (a)providing said object with a pitch sensor having (i) a pitch sensorhousing defining a closed internal chamber, (ii) an arrangement ofelectrically conductive members in a predetermined positionalrelationship to one another within the chamber, and (iii) a flowablematerial contained within said chamber and through which electricalconnections between said electrically conductive members are made suchthat, in one mode of operation of the pitch sensor, a first ratio of anelectrical property between a first combination of said members to thecorresponding electrical property between a second combination of saidmembers is indicative of displacement of said flowable material withinsaid chamber and the pitch sensor uses the first ratio to generate anoutput voltage indicative of such material displacement, and such that,in a second mode of operation of the pitch sensor, a second ratio of anelectrical property between a third combination of said members to thecorresponding electrical property between a fourth combination of saidmembers is indicative of displacement of said flowable material withinsaid chamber and the pitch sensor uses the second ratio to generate theoutput voltage indicative of such material displacement and thereby thepitch of said object; (b) operating said pitch sensor in said first modeof operation under first predetermined circumstances so as to generatethe output voltage and thereby determine the pitch of said object undersaid first predetermined circumstances; and (c) operating said pitchsensor in said second mode of operation under other second predeterminedcircumstances so as to generate the output voltage and thereby determinethe pitch of said object under said second predetermined circumstances.11. A method according to claim 10 wherein said first combination ofconductive members is configured such that said pitch sensor is operatedin said first mode when the pitch of the sensor is within a pitch rangeof plus or minus a certain percentage of grade and wherein said secondcombination of conductive members is configured such that said pitchsensor is operated in said second mode when the pitch of the sensor isat a pitch outside said range of plus or minus a certain percentage ofgrade, said first and second predetermined circumstances correspondingto whether said pitch sensor is within or outside said range,respectively.